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•Residues permanence is a dangerous side effect of cleaning of paintings.•Previous analytical methods are not able to non invasively identify the residues.•Reflection FT-IR is ...sensitive and specific for the identification of cleaning residues.•Reflection FT-IR enables a real time, in situ, and non invasive monitoring of surfaces.
The control of surface cleaning procedures of paintings is difficult and residues of cleaning materials can remain on the surface as potential risk factors for the integrity of the original paint layers. Therefore, the development of a suitable analytical strategy for in situ detection of cleaning residues directly on the painting surface is essential.
In the present study, we propose reflection FT-IR spectroscopy as non-invasive tool for monitoring cleaning residues from polychrome surfaces. Tests on simplified model paints allowed defining the analytical strengths both in term of selectivity and detection limits towards thickeners, surfactants and chelating agents most commonly used in cleaning formulations. Subsequently, the detection of these components has been assessed on aged paint mock-ups and an easel painting after cleaning with different gel formulations. The obtained results clearly proved the strengths of reflection FT-IR spectroscopy for a real time, non-invasive detection of cleaning residues on polychrome surfaces. Thickeners such as Klucel® G, surfactants including Ethomeen® C/12 and C/25 and chelating agents (citric acid + TEA, tetrasodium EDTA salt) were clearly detected after dry removal of the gels and in some tests also after the clearance step.
